Question
Being sensitive to indoor/outdoor fertilizer differences I have endeavored to only use indoor fertilizer (I have not yet ventured to outdoor gardening).  Could the salt deposits be caused by watering the plants from the tap?  Thanks.

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Followup To

Question -
I live in New England and have several indoor plants where there is a hard rust-colored buildup at the top edge of the soil on the pot and also in the drainage area.  What is this, causes it, and how can the pots be cleaned for use again?

Answer -
probably salt deposites from using an outdoor fertilizer (like miracle grow - for outdoor use)instead of an indoor type(like miracle grow - for indoor use). switch to an indoor one(peters, miracle grow, etc.).
use a tooth brush and watered down bonami(spell??) cleanser on the outside of the pot. you may have to unpot the plant so you can do the lip of the pot.

Answer
it could be but i would doubt it. check w/your local water supply company to see if other people are having the same problem. make sure your indoor plant food says soluable salts removed or not any soluable salts. the regular miracle grow in the yellow and green container is not for indoor use...